Catalyst
by Phoenix Satori
Summary: Physics, babies. ::Dasey::


Penance for the long absence. I have missed ye all sumfin' fierce.

Anyway, all research papers are done and I should have more to contribute soon. Whether you like it or not. Damn it.

One more thing: I have this thing where I usually forget to add in any context when I write fic, so I'll just mention, by way of clarification, that I'd envisaged this as taking place sometime after graduation, before they leave for college, and after, perhaps, a D-Rock event (I never decided definitively, which is another reason I didn't concern myself with writing too much about it), but definitely some sort of competition. Also, Casey has a mysterious job that I don't bother to identify. Think that's about it.

[Definitely own it. Don't. Definitely _don't_ own it. Damn it. I am _always_ forgetting to add that word.]

**

* * *

**

_::in which Sir Isaac Newton performs a practical demonstration of the laws which govern All Things --even, apparently, teenagers::_

_***_

('_first law of motion is a piece of cake: things don't move 'til they get a shaaaaake_!')

And that's when she does the unthinkable: she _kisses_ him.

(It's not a _real_ kiss, where there are two consenting parties, where there're two sets of lips and electricity and possibly tongue, where there's friction and heat and all the chaos of the Moment. It's a _sisterly_ kiss; her lips at his cheek before he has the chance to twist away, a playful peck in an unintentional moment of camaraderie. The terms 'hot' and 'bothered' manifest suddenly in his mind in troublingly close proximity to 'Casey,' and it is very much Not Okay.)

He does what any other rational, sensible male in his position would do in this sort of situation (or anyway, he does the first thing he can think of): he pushes her away.

(It's a _real_ push; she goes smashing to the ground with a sharp cry, she looks up at him with an expression betraying hurt and confusion and anger, and he doesn't even _care_ if she's okay. He doesn'tdoesn'tdoesn't. He hopes she's broken something because _she_ has broken the _law_.)

"De-_rek!_ What the hell was THAT for?" She's up on her feet in an instant, and she shoves him right back. Then, he thinks because he's been staring at it, she realizes her dress is grass-stained. "Ahh! _De-rek_! This was a _brand new dress_!" She traces the stain as it crosses over her hip and smudges across her ass, and his mouth goes dry. "Why did you _push_ me, you JERK?" She shoves him again and he barely even feels it.

(He thinks he might be having one of those out-of-body experiences; it feels like he's watching this whole horrible thing happening, and he's totally powerless to _stop it_.)

"Derek! Earth to _Derek_!" She snaps her fingers right in front of his face, and he takes a step back.

"WHAT is your PROBLEM?" He explodes after a moment, and the way she flinches almost makes him think he's over-reacted. (But of course he _hasn't_; if anyone's been paying attention, Casey has just _kissed_ him.)

"My-MY problem?" She yells back, just as vehemently ('_third law of motion gives you satisfaction: for every force made there's an opposite reaction_!'). "You _do_ realize you just assaulted me for no apparent reason!" She huffs, hands balling into fists, cheeks pinking, eyes lighting up. (Derek Venturi, ladies and gentlemen, the Deeply and Profoundly Aloof and Impervious!) "I didn't even DO anything to you!" Hurt is winning out over all the other emotions he's _used_ to seeing her display in a confrontation between the two of them. It is extremely disturbing. (Parental guidance recommended.)

"Case," he begins, then reminds himself that this is all Her Fault; she has no right to threaten tears to turn this situation in her favor. Unfortunately: "You aren't even supposed to _be here_!" –is the only thing he can come up with on the spot to retaliate.

She looks –there's no other word for it—stricken. Dejected. (But also _incensed_, so everything is still okay.)

"_You_ were the one who ASKED me to come, remember? You didn't have any favors to call in and I still _came for you_ when you asked. We WON, Derek! Can't you even _pretend_ to be grateful?" His jaw sets and he can barely understand what she's saying (because he can't take his eyes off of her _mouth_).

"You're right, we did win. Your job's over. You can be on your way now." Her mouth opens, shuts again. Her eyes are watering and (_ohshitohshit_) she's going to cry. And hey, hello, Casey, that's _cheating_. (Not that he doesn't condone or approve of cheating; it's just that _he's_ supposed to be the only one allowed to do it.)

Maybe his mental panic reaches her, after all, because she inhales deeply, shakily (her eyes are closed and her whole body follows the motion of her breath, and he finds himself accidentally riveted), and the waterworks are over before they've even begun. She doesn't leave, either, though, and even as one crisis is averted another manifests. (You know, the one where she's _still there_ and is apparently _refusing to leave_.)

"That was your cue to go, Spacey." He makes a shooing motion with his hands and she appears unimpressed.

"I don't take cues from _you_," she sneers, and gets in his face (and _why_ must bad things happen to good people?), "and I'm not going _anywhere _until you thank me."

"_What_?"

"You said it yourself," She smiles maliciously and his stomach twists painfully, "you said you 'owed me big time.' That was part of the deal." Had he actually _said_ that? Surely he would have remembered saying something so obviously insane.

"You can't prove anything." He scoffs.

"You _listen to me_, Derek," she slices through another few inches of space between them and pokes her finger against his chest, "you _said_ that you owed me a favor, and whether or not you actually meant it is not my concern. Because regardless of if you did or not, the truth of the matter is that you _are_ in my debt. And you can let me take the high road and just pay up, _or_ we can do this the hard way and I'll start sorting through my blackmail material and I can _force_ you to pay up." He thinks it's possibly due to the fact that her unique-form of Casey-engineered psychosis is contagious that he finds her tirade rather inviting. ('Rather inviting' only because the _actual_ term his mind uses is inappropriate for audiences under 13 years of age.) At the last second, out of sheer force of habit, he remembers to glare at her.

"What do you want?" He grumbles resignedly.

"I already told you: look me in the eye, and _thank me_." He's about to reintroduce himself to her, because she appears to have forgotten who he is, when she makes the terms sweeter still, "AND," that Malevolent Bitch smile twists back onto her face, and this is why you don't mess with _crazy people_, "you have to _mean it._" He stares at her for a long moment, in case she's just taking a dramatic pause before she delivers the punch line.

"Casey," he says very patiently, and sets a hand on her shoulder (which is irritatingly bare and even more irritatingly soft), "I…" her expression is eager, morphing swiftly from scheming to excited, and, because he's feeling especially Bastard today, he's not even a little guilty about crushing her hope, "I am…" he casts his eyes sideways, affecting Sudden Self-Consciousness (and _damn it_ he is good at this; he's impressed with himself for such an award-winning performance in the immediate aftermath of Recent Trauma) "I am…_so_ not going to do that." He explains, very seriously, looking at her in vague pity while her face transforms again, this time with anger. "But I want you to know," he adds quickly, "that it's _only_ because I am not physically capable of such a thing." She does this eye-tic thing that makes her look vaguely homicidal. So he knows there's something wrong with him when the vocabulary item 'adorable' spontaneously appears in his mind. (Speak of this to no one.)

"Would it _kill_ you to be decent to me once in a while?" Her fingers are fisted at her sides. Somehow the idea of her slugging him is extremely hilarious. He wonders if that's what she's planning.

"It might." He says earnestly.

"I can't _believe_ you, Derek! I came here in the _middle_ of my _shift_ to come help you –do you have any _idea_ how hard it is to get someone to cover for you _mid-shift_? Do you not even care what I had to _promise_ Mel I would _do_ if she'd come fill in for me? I had to pick up _three extra shifts_! THREE! All so I could be _here_, where my stupid moron step-brother could _push_ me for no reason at all and ruin my dress and then refuse to apologize or explain or even be properly blackmailed into giving me the thanks I deserve _anyway_, since _I'm_ the reason we won at all!" He wants to tell her she sounds like a conceited brat, but she's breathing somewhat heavily and he gets distracted. "And we were…we were…getting along! Or something! Sort of! Just when I think you're _maybe_ not as bad as you seem—" (wait-a-minute.)

"Woah, woah, when was this? I have given no such impressions."

"DE-REK!"

He opens his mouth, closes it again. He'd been about to tell her to 'calm down,' when he remembered that night (so long ago now) in their shared bathroom, how they'd ended up covered in goop and locked around each other in a grappling match on the floor—

"Calm down." Casey stiffens.

(this split-second decision happily brought to you by: Insanity!)

"_What_ did you say?" she says, Very Calmly (in the same voice a sociopath might employ to inform a puppy of Imminent Kicking).

"I said," he takes a measured step forward, enough to be encroaching without actually crossing any lines, "to _calm down_."

(_'second law of motion is all about the force; if something hits hard then the object takes that course!'_)

The instant before she steps in to shove him he makes up his mind, and he smirks when her hands flatten against his chest and doesn't try to catch himself when the force of the blow knocks him backwards. Instead, he locks his fingers around Casey's forearms and lets the momentum carry her to the ground _with him_. She shrieks, and purely out of instinct, he rolls to absorb the shock of the impact, tucking her temporarily against him as he spins them. She still crash-lands on top of him, and for one tense moment they're stuck staring at each other, wide-eyed, from a rough distance of approximately half a centimeter, until at long last the planets realign and they start wrestling in earnest, and from there it's just a tangle of limbs and '_De-reks_!'

Until, you know, it _isn't_, until it's quite a bit more than that, but that's really not his fault: _she started it_, let's remember, and her dress doesn't have _sleeves_ and her eyes are all glittery and blue and her hair keeps falling between them and getting stuck in his mouth, and she keeps making these soft, frustrated sounds –no, this is definitely all on her.

So, really, it's perfectly alright that he's making out with his step-sister in the middle of a public venue, on the ground, covered in grass and dirt and positively surrounded by the small group of people who'd gathered to watch them argue, including several mutual friends and acquaintances, and by now? Probably also their family.

(He hopes this counts as a 'thank you,' because otherwise she's going to be very annoying later.)

* * *

Apparently the PDA thing is not as big a deal when there's a Casey involved.

So, funny story. This _was_ going to be a one-shot in University Steps. But it turned into something entirely different than I had intended, and then I couldn't figure out how to resolve it without the making out. Anyway, didn't fit the continuum right, and I'm not ready for anything to happen..._quite_ yet in USteps, so I just threw this one out to stand on its own.

And now I must go drown myself in caffeine.


End file.
